Linear polymers of carbon monoxide with one or more olefinically unsaturated compounds are made up of the polymer units from carbon monoxide on the one hand and the units from the olefinically unsaturated compounds on the other hand which are present in a substantially alternating arrangement. These polymers can be prepared by contacting the monomers at elevated temperature and pressure with a catalyst composition containing a Group VIII metal and a phosphorus bidentate ligand with the general formula (R.sub.1).sub.2 P-R-P(R.sub.1).sub.2 in which R.sub.1 represents an optionally polar substituted monovalent hydrocarbon group, and R is a divalent organic bridging group containing three or four atoms, of which at least two are carbon atoms, which connects the two phosphorus atoms with each other. Both cyclic and acyclic groups may be used as R.sub.1 groups. An example of a phosphorus bidentate ligand in which the R.sub.1 groups possess a cyclic structure is 1,3-bis(diphenylphosphino)propane. As an example of a phosphorus bidentate ligand in which the R.sub.1 groups possess an acyclic structure, 1,4-bis(di n-butylphosphino)butane can be mentioned.
During an investigation recently carried out by the applicant into the preparation of the above-mentioned alternating polymers, it was found that the number of atoms in the bridge connecting the two phosphorus atoms of the bidentate ligand with each other has a large influence on the polymerization activity of the catalyst compositions. For example, it was found that in the polymerization of carbon monoxide with ethene and/or with one or more .alpha.-olefins with at least three carbon atoms per molecule (designated herein as C.sub.3+ .alpha.-olefins) using a catalyst composition containing a tetra-aryl bisphosphine, a sharp decrease in the polymerization activity occurred if a bisphosphine with three atoms in the bridge was replaced by one with four atoms in the bridge. A corresponding decrease of the polymerization activity was observed if, in the polymerization of carbon monoxide with ethene using a catalyst composition containing a tetra-alkyl bisphosphine, a bisphosphine with three atoms in the bridge was replaced by one with four atoms in the bridge. In complete contrast with this, it was found that in the polymerization of carbon monoxide with one or more C.sub.3+ .alpha.-olefins and optionally also with ethene using a catalyst composition containing a tetra-alkyl bisphosphine, a sharp increase in the polymerization activity occurred if a bisphosphine with three atoms in the bridge was replaced by one with four atoms in the bridge.
In the course of continued research by the applicant into this subject, a class of diphosphorus compounds has now been found which have shown themselves to be ideally suited, together with a Group VIII metal, for use in catalyst compositions intended for the preparation of the above-mentioned alternating polymers. In contrast with the previously mentioned bisphosphines with the general formula (R.sub.1).sub.2 P-R-P(R.sub.1).sub.2 in which either two cyclic groups or two acyclic groups occurred at each of the phosphorus atoms as R.sub.1 groups, in the present diphosphorus compounds each of the phosphorus atoms forms part of a separate monocyclic structure in which a phosphorus atom occurs together with five carbon atoms. The present diphosphorus compounds can be represented by the general formula X-R-X in which X represents a phosphacyclohexyl group which is connected via the phosphorus atom with a carbon atom of the bridging group R, and R has the previously indicated meaning.
It was found during the investigation that the catalyst compositions which contained a diphosphorus compound with the general formula X-R-X exhibited the same special behavior with the number of atoms in the bridge as the catalyst compositions which contained a tetra-alkyl bisphosphine. On replacing in the catalyst composition a diphosphorus compound with three atoms in the bridge by one with four atoms in the bridge, a sharp decrease in the polymerization activity takes place if the catalyst composition is used for the polymerization of carbon monoxide with ethene, while such a replacement leads to a sharp increase in the polymerization activity if the catalyst composition is used for the polymerization of carbon monoxide with one or more C.sub.3+ .alpha.-olefins and optionally also with ethene. It was further found in the investigation that the catalyst compositions containing a diphosphorus compound with the general formula X-R-X in which the bridge contains four atoms also displayed an exceptionally high polymerization activity when used for the polymerization of carbon monoxide with ethene and with a C.sub.30+ .alpha.-olefin, bearing in mind the polymerization activities of these catalyst compositions in the polymerization of carbon monoxide with ethene or with the relevant C.sub.3+ .alpha.-olefin.
As well as for the preparation of alternating polymers of carbon monoxide with ethene and/or with one or more C.sub.3+ .alpha.-olefins, the catalyst compositions which contain a Group VIII metal and a diphosphorus compound with the general formula X-R-X can also be used for the preparation of alternating polymers of carbon monoxide with other olefinically unsaturated compounds.
A novel catalyst composition which contains a Group VIII metal and a diphosphorus compound with the general formula X-R-X, where R is a divalent organic bridging group and this bridge connecting the two phosphorus atoms present in the diphosphorus compound with each other allows for the diphosphorus compound to contain three or four atoms of which at least two are carbon atoms, and X represents a phosphacyclohexyl group which is connected via the phosphorus atom to a carbon atom of the bridging group R.